1. Field of the Invention
This invention is directed to a combined roll which is highly resistant to thermal shock.
2. Description of the Related Art
Combined rolls are useful as structural members in rolling apparatus and are generally made of iron and steel or a non-ferrous alloy such as copper alloy, aluminum alloy or the like.
An example of the above-mentioned combined roll is disclosed in Japanese Examined Patent Publication No. 6-99776. This combined roll has an external ring portion made from a tungsten carbide-based cemented carbide (hereinafter referred to simply as "a cemented carbide") and an internal ring portion made from ductile iron and casted to the external ring portion. Because of the casting, a metallurgical bond is formed between the external and internal rings.
Recently, high performance and high power have become important in the field of combined rolls. The result is an increase in both rolling speed and reduction ratio. Because the surface of a pressure roll is not always in contact with the material to be rolled, any increase in the rolling speed and reduction ratio subject the pressure roll to severe and repeated thermal shock. Under such strict operating conditions, conventional combined rolls, such as those mentioned above, may break due to their insufficient resistance to thermal shock.